The Poacher and the Gamekeeper: Synchronization Delivery and AssuranceKen Hann, Director, R&D June 2016
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Contents
Synchronization
• Delivery vs monitoring• Requirements• Motivation
• Monitoring the real world• APST (PTP back-up for GNSS)
• Physical vs built-in probes• Writing the rulebook
Synchronization Delivery vs Monitoring
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Monitoring a Time ServiceDid you see his face when you
mentioned SLAs?
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Given a reference – suitable equipment can provide:
1. A distribution solutionPoacher:”Fresh sync” with innovation
2. An assured solution Gamekeeper:Synchronization by the book
3. Both?
Synchronization service hand-off
Synchronization to nearby nodes
Statistics to NMS
SLA
Synchronization to nearby nodes
Synchronization – Delivery or Assurance?
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Telecom Profile Delivery Requirement Monitoring
Frequency G.826X
16ppb FFP>1%(150us in
200s)Phase G.827X
1.5usec ?Phase G.82XX
<100nsec ?
Question 1: Should standards support monitoring PTP phase networks?
Synchronization Delivery andMonitoring Requirements
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The Time Problem ...
Aggregation Island
Base-station Island
Best-Effort Beach
Asymmetry Shark
“Try G.8275.1, my boy”!
Core
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Another Way of Looking at AsymmetryT1 – Sync message timestamped according to master clockT2 – Sync message timestamped according to slave PTP clockT3 – Delay request message timestamped according to slave clock T4 – Delay request PTP clock
T2 = T1 + Delay_MS + OffsetT4 = T3 + Delay_SM – Offset
Symmetry: Delay_MS = Delay_SM = Delay Offset = ((T2-T1)-(T4-T3))/2
Asymmetry: Delay_MS != Delay_SM :Offset+(Delay_MS-Delay_SM)/2=(T2-T1)-(T4-T3))/2
SlaveMaster
Sync (T1)
Delay_Resp (T4)
Delay_Req
T1
T2
T3
T4
T4
Delay_MS
Delay_SM
Offset from master
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1) Bypass the problem:• Grandmaster closer to the slave• Use full on path support where possible• Use sync probes to monitor performance
Slave
Base Station / Small Cell
GrandMaster
GNSS
Probe
Mobile Network Operator
The Solution(s)
2) Compensate for fixed asymmetries
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12%
52%
36% not important
mandatoryinteresting op-tion
Operators Survey – Synchronization Assurance (“Gamekeeping”)Do you rate synchronization service assurance as an important tool for delivering mobile backhaul services?
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Why Is “In-Service” Sync Assurance Needed?• Making sure synchronization works is not trivial • Network PDV and asymmetry impact synchronization quality• SLA 1-way delay monitoring using OAM/OWAMP or PTP• Requires equipment to collect data (probes)• Needs OSS/NMS to check alarms and performance• Synchronization monitoring tools should be part of delivery
How well does sync work?
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Examples of Delivery and Monitoring1. Monitoring slave/BCMonitoring sync service
2. APTSBacking up local GM
Synchronization service hand-offSLASynchronization
service providersnetwork
Synchronization to nearby nodes
Statistics to NMS
Synchronization backup
Synchronization to nearby nodes
Statistics to NMS
PTPgrandmaster
Monitoring The Real World
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Large DGNSS protects against “double jamming” events
T-GM
GNSS
PTPGrandmaster
Network
APTSmini-GM
LocalBase Station
GNSS
RemoteBase Station
T-SC
T-SC
T-SC
T-SC
Antenna separation distanceDGNSS
GNSS Jamming – Antenna Separation Distance
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GNSS Jamming – Antenna Separation Distance
”Practically perfect” PTP networks ... are also vulnerable
T-GM
GNSS
PTPGrandmaster
Network
APTSmini-GM
LocalBase Station
GNSS
RemoteBase Station
T-SC
T-SC
T-SC
T-SC
Antenna separation distanceDGNSS
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T-GM
GNSS
PTPGrandmaster
Network
APTSmini-GM
LocalBase Station
GNSS
RemoteBase Station
T-SC
T-SC
T-SC
T-SC
Antenna separation distanceDGNSS
Some Networks Aren’t Perfect ...
Large DGNSS but is the network good enough?
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Assisted Partial Timing SupportAn Example of Delivery and MonitoringWhen GNSS is available it:
1. Supports the local time base
2. Allows monitoring of PTP slave timestamps
3. Calculation of assymetry, etc.
PTP clocks are not stressed when GNSS is available
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PRTC
GNSS
Slave
TE /TIE
PPS PPS
MTIE
TIE TE
TDEV Total TE dTE cTE
KPI 1 KPI 2 KPI 3 KPI 4 KPI 5
Asymmetry Metrics
PTP
KPI 6
PTP
TE / TIE
SyncE
EEC
CLK
APTS – Monitoring Using GNSS Reference
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APTS – KPIs and SLA• PRTC vs PTP slave recovered clock (PTP input) • Total/constant/dynamic time error (TE) vs predefined threshold • MTIE vs predefined mask• Network asymmetry and PDV
• PRTC vs Sync-E• MTIE vs predefined mask
• Results and alarms are collected by NMS• Helps in early detection of primary and secondary errors
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APTS – GNSS Failed
When GNSS fails:1. PTP maintains the local timebase 2. Prior assymetry can be comphensated3. Increased sensitivity to temperature
PTPQuestion 2: What about reversing roles, i.e. PTP primary and GNSS backup?
Probing Functions
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• A sync probe compares a selected port to a reference (GNSS)• The port can be a physical input; or T3 monitoring; slave monitoring• SLA monitoring and brownfield applications
Sync Probe CLK, 1PPS MTIE & Packet MTIE
CLK TIE, 1PPS TE & Packet TE
10MHz
1PPS
BITS
Sync-E
Physical Clock Ports
T3
Ethernet Ports
T1T4
T1T4
T3
GPS
Slave Port Master Port
Add Physical Probe Devices to the Network
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• A Sync probe function compares a selected port to a reference• The port can be a PTP clock or monitoring instance• Delivery and monitoring functions co-exist on the same Ethernet port
Sync Delivery Sync Probe
Packet MTIE
Packet TE
Single Ethernet Port
Sync-E T3
T1T4
T1T4
T3
BMCA MonA Mon B
Embedded Probe Functions in Every Ethernet Port ...
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T-GM
GNSS
Slave
T-BC T-BC T-BC T-BCT3 T3 T3 T3 T3
Self Monitoring Chain Using T3• G.8275.1 can support long chains of BC (i.e. 20 hops)• Monitoring can be included based upon returned T3• Each BC compares own clock with downstream neighbor• May need PTP monitoring functions in each port (if no valid T3)
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In-Circuit Monitoring...Can We Learn From Circuit Switching1. Assured, low bit error rate circuits2. BER statistics defined (G.821 and G.826)
• Bit errors block errors• Available time/unavailable time• (Severely) errored seconds• Degraded minutes• 15min/24h BER records
3. Non-intrusive monitoring (overhead bits)4. Trouble shooting mechanisms (loopbacks)5. Monitoring integrated to nodes (PRBS generators/analysers)6. Switching monitoring resources onto unused channels
Goal
Standards
Vendors
Synchronization monitoring is still early days
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Self Monitoring Complex Topologies (Open for Ideas)• G.8275.1 can support large and complex structures of BCs • Each BC port supports: distribution and monitoring input/output
T-BC
T-BC
T-BC
T-BC
T-GM Slave
Question 3: Who will define in-ciruit monitoring?
BMCA
Mon-A
Mon-B
Only monitoring
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• Simultaneous probing across network• Dedicated “GNSS probes” on edge• Integrated probes ?
Network(DUT)
T1T4
T3
T1T4
CLK, 1PPS MTIE & Packet MTIE
CLK TIE, 1PPS TE & Packet TE
T3
T-GM
1PPS
10MHz/BITS/Sync-E
PTP network Probe Statistics and Usability Score
Sync Probe
Sync Probe
Sync Probe
Sync Probe
GPS
Assuring Quality and Correlating Testing
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Summary(The “Poacher” and the “Gamekeeper”)
The “Poacher”• Innovates to provide sync
The “Gamekeeper”• Enforces the rules for assured sync delivery• We need to write the rules
• Today – probes monitor clocks and network/service• Tomorrow – probes integrated into delivery systems
Thank [email protected] Hann, Director, R&D
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